A novel blue-emitting Zn(II) MOF featuring parallel 2D+2D interpenetrated layers and tubelike channels was generated and shown to efficiently accommodate lanthanide(III) cations (Ln3+ = Eu3+, Tb3+, or a mixture of Eu3+/Tb3+), resulting in the Ln3+-encapsulated functional materials with a tunable emission color, including red, green, and nearly pure white light. Furthermore, the thermal-responsive luminescence was investigated for the lanthanide-codoped MOF to exhibit the chromic transition from white at room temperature to blue around liquid nitrogen temperature.

Heterometallic Zn2Ln2 [Ln = Gd (1), Eu (2), Tb (3), Dy (4)] discrete molecules with edge-defective cubane structure are assembled from a multifunctional fluorescent conjugate ligand and LnIII/ZnII mixed-metal ions; they exhibit the tunable luminescence, including ligand-based yellow-green light emission for 1 and 4 and lanthanide-center emission for 2 and 3. The multiple stimuli-responsive photoluminescences were investigated to show a two-step thermal-responsive luminescence increase in the intensity upon cooling and piezochromic luminescence.

•8-Hydroxyquinoline carbohydrazone were prepared for dinuclear Dy(III) single molecule magnet.•Coordination anion controlled dinuclear Dy(III) compounds were obtained.•Dinuclear Dy(III) compounds showed the anion-dependent SMM property.The employment of an 8-hydroxyquinoline carbohydrazone tetradentate ligand, 8-hydroxyquinoline-2-carboxaldehyde-(benzoyl)hydrazone (H2L), DyCl3·6H2O and Et3N has led to the formation of dinuclear Dy(III) complex [Dy2(HL)2Cl4(CH3OH)2], (1) and [Dy2(HL)2((PhO)2PO2)4]·2(CH3OH) (2) in the presence of excess amount of bridging diphenyl phosphate anion, (PhO)2PO2 −. X-ray crystallography data revealed that two DyIII atoms in 1 are doubly bridged by the two phenolato oxygen atoms of HL− ligands, however, the DyIII atoms are bridged by additional two deprotonated μ1,3-phosphate anions in 2. Each of the two lanthanide ions is eight-coordinated and is located in the different symmetry with triangular dodecahedron (D2d) for DyIII in 1 and elongated triangular bipyramid (D3h) for DyIII in 2. Dc magnetic susceptibility studies in the 2–300 K range reveal the weak antiferromagnetic interaction for 1 and 2. Both of them showed field-induced slow magnetic relaxation behavior with the Ueff for 1 of 46.0 K higher than 36.8 K for 2.The carbohydrazone tetradentate ligand was emplyed for the assembly of coordination anion controllable Dy(III)-based SMM.Download high-res image (204KB)Download full-size image

The reaction of the multisite coordination ligand (H2L) with Co(Ac)2·4H2O in the absence of any base affords a homometallic tetranuclear mixed-valence complex, [Co4(L)4(CH3CO2)2(CH3OH)2]·Et2O (1). This mixed-valence metallogrid [Co4(L)4(CH3CO2)2 (CH3OH)2]·Et2O (1) has been theoretically and experimentally analyzed to assign the valence and spin state in the form of trans-[CoIIIls–CoIIhs–CoIIIls–CoIIhs]. HF-EPR reveals the presence of axial anisotropy (D = −34.4 cm−1) with a significant transverse component (E = 9.5 cm−1) in the local high spin cobalt centers. Slow magnetic relaxation effects were observed in the presence of a dc field, demonstrating field-induced single ion magnetic behavior, which is associated with the unusual electronic structure of Co(II) within the metallogrid.

A self-assembled cobalt molecular grid of a pyrazine-bridged bis-tridentate ligand (LR), where R = H (1), CH3 (2), and Br (3), was prepared and structurally characterized. Depending on the electronic effects of the substituents on the ligand, the redox of the metal center was systematically modulated, and the magnetic behavior from essentially high-spin CoII in 3 versus completely diamagnetic CoIII in 1 to CoII spin-crossover in 2 can be achieved.

Structural assembly and reversible transformation between a metallogrid Dy4 SMM (2) and its fragment Dy2 (1) were established in the different solvent media. The zero-field magnetization relaxation was slowed for dysprosium metallogrid (2) with relaxation barrier of Ueff = 61.3 K when compared to Dy2 (1). Both magnetic dilution and application of a moderate magnetic field suppress ground-state quantum tunneling of magnetization and result in an enhanced Ueff of 119.9 and 96.7 K for 2, respectively. Interestingly, the lanthanide metallogrid complex (2) exhibits magnetic hysteresis loop even up to 16 K at a given field sweep rate of 500 Oe/s.

Dihydroquinazoline FeII complexes, namely [Fe(pq-R)2](X)2·xCH3OH·yCH3CN·zH2O (R = 2-py: X = ClO4−, x = 1, y = 0, z = 2 (1), BF4−, x = 0, y = 2, z = 1.75 (2), CF3SO3−, x = 1, y = 1, z = 0 (3); and X = ClO4−: R = 2-OCH3, x = 0, y = 0, z = 1 (4), R = 3-OCH3, x = 0, y = 0, z = 1 (5)), were prepared and the effects of the solvent, counteranion and ligand substituent on spin crossover properties were discussed. Comparison of X-ray diffraction data for these complexes revealed the sole presence of high-spin FeII at 298 K and the bond distances around the FeII center at low temperature fall much closer to those at high temperature, which is consistent with variable-temperature dc magnetic susceptibility data. However, the loss of solvent induced a significant change in the spin state of complexes 1 and 2. Moreover, fits to magnetic data of the desolvated samples provide crossover temperatures of T1/2 = 182.9(6), 157.0(8) and 138.3(5) K for 1-des (ClO4−), 2-des (BF4−) and 3-des (CF3SO3−), respectively, indicative of the anion-dependent transition temperature. The cooperativity operating in the complexes is thought to be mainly from the intermolecular π⋯π interactions between dihydroquinazoline rings on the neighboring molecules. The ligand substituent effect was also investigated on FeII SCO properties. This work revealed the spin crossover properties of new types of dihydroquinazoline Fe(II) complexes, including the transition temperature, the degree of completion and the cooperative nature of the transition, which can be optimally designed when developing new spin-crossover materials.

A remarkably stable tubular 3D Zn-MOF with hexagonal channels and a rare ptr topology was prepared under solvothermal conditions for liquid and vapor phase adsorption and separation of the C6–8 aromatic compounds. The material showed preferential affinity for benzene and can effectively separate benzene from its organic analogues under ambient conditions in both vapor and liquid phases. Furthermore, it exhibited preferable uptake of p-xylene over other C8 xylenes.

Two one-dimensional (1-D) chain complexes with pentagonal bipyramidal DyIII centers have been synthesized and magnetically characterized. Field-induced single molecule magnet behavior has been revealed in both compounds, which is still rarely reported in a lanthanide compound with a pentagonal bipyramidal coordination geometry. Their crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation.

The reaction between the rhodamine-6G-2-(hydrozinomethyl) quinolin-8-ol (HQR1) ligand and Ln(tta)3·2H2O precursors (tta = 2-thenoyltrifluoroacetone) leads to the formation of a series of mononuclear complexes with formula [Ln(QR1)(tta)2]·(CH3OH)x(H2O)y (3–6) for (Ln = Yb, x = 1, y = 0 for 3; Ln = Dy, x = 1, y = 0.5 for 4; Ln = Tb, x = 2, y = 0 for 5; Ln = Ho, x = 2, y = 0 for 6) together with [Dy(QR1)2][NO3]·(CH3OH)(H2O) (2) and the reported [Yb(QR1)2][NO3]·(CH3OH)(H2O)0.5 (1), for the purpose of magnetic comparison. Their X-ray structures revealed that the coordination environment of each Ln(III) center is filled by two tta carboxylate groups and a tetrachelate N2O2 binding site coming from the deprotonated HQR1 ligand. The Yb and Dy complexes showed the field-induced slow relaxation of magnetization. Both Yb(III)-containing compounds were characterized by X-band EPR and magnetism studies, which revealed the different effective g values and slow paramagnetic relaxation. Comparison between two Yb(III) complexes 1 and 3 shows that the magnetoanisotropy and the barrier height of the magnetic relaxation are sensitive to the subtle change in the coordination environment of the central metal ion. However, in Dy3+ series, QTM is difficult to overcome even under the dc field and the subtle variation of the coordination environment leads to a tiny change in the energy barrier of slow magnetization relaxation. These results show that ligand-donating ability while maintaining molecular symmetry can be controlled to design single molecule magnets with enhanced relaxation barriers.

A series of transition metal(II) complexes of the type [M(PPQ)2] [PPQ = 2-pyridine-2-yl-3(pyridine-2-methylene-amino)quinazolin-4(3H)-one, M = Co(II), Cu(II), Ni(II), Zn(II), Cd(II)] have been prepared and characterized by IR spectroscopy, elemental analyses and X-ray crystal diffraction. The crystal structure studies revealed diverse coordination behavior of PPQ toward different metal ions, acting as an NNO donor in the cobalt(II) and zinc(II) complexes, but an NNN and NNO mixed donor in the copper(II) and nickel(II) complexes. The metal center generally has an octahedral coordination geometry with the tridentate PPQ ligand, except for the Cd(II) complex in which two PPQ ligands and a nitrate are coordinated (N4O4), forming a distorted triangular dodecahedron. The thermal stabilities, luminescence and magnetic properties of these complexes have been studied.

The reactions of ligand N′-[(pyridin-2-yl)methylene]pyrazine-2-carbohydrazide (ppcd) with different copper salts (1, acetate; 2, perchlorate; 3, sulfate) in MeOH could afford one acetate-bridge tetranuclear discrete [Cu2(ppcd)(ac)2(H2O)(OH)]2·H2O (1), one-dimensional (1D) chiral chain [Cu(ppcd)]ClO4 (2), and a 1D-decker complex of a trinuclear copper(II) subunit, Cu3(ppcd)2(H2O)4(SO4)2 (3). Single-crystal X-ray analysis revealed that conformation isomerism of the ppcd ligand was associated with the configuration of −N–N– (trans or cis) and could induce the versatile coordination mode in the presence of different anions. The 1D chiral chain was interestingly obtained from the achiral rigid ligand in complex 2. Magnetic studies indicated that the magnitude of the antiferromagnetic coupling can be tuned because of the configuration isomerism [compound 1 is practically diamagnetic at room temperature (J ≈ −1000 cm–1), with a strong antiferromagnetic one (J = −255.4 cm–1) for 2 in the 1D uniform chain and an antiferromagnetic one (J = −123.6 cm–1) for 3 within the trinuclear copper subunit].

Two cobalt mixed-valence complexes with different substituents have been prepared and structurally characterized by single-crystal X-ray diffraction to alter slow magnetic relaxation by tailoring the transverse anisotropy. The trinuclear complexes [(L1)4Co3(H2O)2](NO3)4·CH3OH·5H2O (1-NO3) and [(L2)4Co3(H2O)2](NO3)4·6H2O (2-NO3) feature a distorted octahedral Co(II) strongly hindered in a trinuclear CoIII–CoII–CoIII mixed-valence array. Detailed magnetic studies of 1-NO3 and 2-NO3 have been conducted using direct- and alternating-current magnetic susceptibility data. In accordance with variable-field magnetic susceptibility data at low temperatures, high-field electron paramagnetic resonance (HF-EPR) spectroscopy reveals the presence of an easy-plane anisotropy (D > 0) with a significant transverse component, E, in complexes 1-NO3 and 2-NO3. These findings indicate that the onset of the variation of distortion within complex 2-NO3 leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior. Consequently, the anisotropy energy scale associated with the relaxation barrier, 5.46 cm–1 (τo = 1.03 × 10–5 s), is determined by the transverse E term. The results demonstrate that slow magnetic relaxation can be switched through optimization of the transverse anisotropy associated with magnetic ions that possess easy-plane anisotropy.

The reaction of the multisite coordination ligand (H2L) with Co(Ac)2·4H2O in the absence of any base affords a homometallic tetranuclear mixed-valence complex, [Co4(L)4(CH3CO2)2(CH3OH)2]·Et2O (1). This mixed-valence metallogrid [Co4(L)4(CH3CO2)2 (CH3OH)2]·Et2O (1) has been theoretically and experimentally analyzed to assign the valence and spin state in the form of trans-[CoIIIls–CoIIhs–CoIIIls–CoIIhs]. HF-EPR reveals the presence of axial anisotropy (D = −34.4 cm−1) with a significant transverse component (E = 9.5 cm−1) in the local high spin cobalt centers. Slow magnetic relaxation effects were observed in the presence of a dc field, demonstrating field-induced single ion magnetic behavior, which is associated with the unusual electronic structure of Co(II) within the metallogrid.

The recent upsurge in molecular magnetism reflects its application in the areas of sensors and molecular switches. Thermal hysteresis is crucial to the molecular bistability and information storage, a wide hysteresis near room temperature is expected to be of practical sense for the molecular compound. In this work, spin crossover iron(II) complexes [Fe(Liq)2](BF4)2·(CH3CH2)2O (1-Et2O) and [Fe(Liq)2](BF4)2·3H2O (1-3H2O) were prepared and structurally and magnetically analysed. The single-crystal-to-single-crystal (SCSC) solvation transformation and the influence on the crystal structures and magnetic hysteresis were investigated in an etherification–hydration cycle. At room temperature, X-ray diffraction experiments indicated a transformation from one crystal (1-Et2O, P21212) to another crystal (1-3H2O, P212121) upon humidity exposure and reversible recovery of its crystallinity upon exposure to ether vapor. The etherified phase 1-Et2O exhibits room temperature spin crossover (T1/2 = 305 K) but negligible thermal hysteresis, however the hydrated phase 1-3H2O exhibits the apparent hysteresis loop (T1/2↑ = 346 K, T1/2↓ = 326 K) which expands to room temperature. This effect is associated with the change of intermolecular cooperativity in the etherification–hydration recyclability.

Two one-dimensional (1-D) chain complexes with pentagonal bipyramidal DyIII centers have been synthesized and magnetically characterized. Field-induced single molecule magnet behavior has been revealed in both compounds, which is still rarely reported in a lanthanide compound with a pentagonal bipyramidal coordination geometry. Their crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation.